Prior art round balers generally have a bale forming chamber defined by an apron comprising an array of side-by-side belts, transverse slats trained on chains, a plurality of rolls or a combination of these various elements, e.g., rolls and belts. Crop material, such as hay, is picked up from the ground, as the baler travels across the field, and is fed into a fixed or expandable chamber where it is rolled up to form a compact cylindrical hay package. While still inside the bale forming chamber in its compacted form, the outer surface of the package is wrapped with twine or web material, such as net, prior to ejecting the wrapped bale from the chamber onto the ground for subsequent handling.
Exemplary of prior art round balers of the general type mentioned above is the baler disclosed in U.S. Pat. No. 4,956,968 issued in the name of K. R. Underhill on Sep. 18, 1990. In this baler an apron consisting of a combination of rolls and belts is used for bale formation. The baler also includes a mechanism for supplying net to a dispensing assembly which in turn feeds the net material into the bale forming chamber for circumferentially wrapping a formed cylindrical bale. The dispensing mechanism includes a net insertion arrangement having a grasping portion for pulling net from the supply mechanism and inserting the free edge, commonly referred to as the tail, into the chamber. Subsequent to wrapping, the net material is severed by a cutting device.
During various phases of the net feeding and wrapping operation in round balers of this general type a restraining force is applied to the net. This force varies in prior art devices from a substantial braking force providing a significant drag to hold the net under tension for cutting to a minimal force to merely avoid unwanted feeding of slack caused by inertial forces due to the tendency of the supply rolls and/or the rolls along the feed path of various systems to overrun. Examples of prior art devices include the disclosure in U.S. Pat. No. 4,604,848, issued Aug. 12, 1986, showing a braking rod continuously urged against the net supply roll. This system also discloses an additional tensioning system which incorporates the use of a moveable roller, about which the net is wrapped, for applying high web tensioning during cutting or tight wrapping. U.S. Pat. No. 4,697,402, issued Oct. 6, 1987, also shows the use of a rod urged against a net supply roll in conjunction with a net feed tensioning system.
Problems have been encountered in past attempts to accomplish, by simple and reliable means, consistent net tension at a desirable level and during a proper duration while the wrapping operation takes place. It is crucial in net systems that both a continuous minimal tension be applied to enhance the feeding function, and a greater uniform braking force be subsequently applied during net cutting. A drawback of many prior art systems is the complexity of the mechanisms involved and the need to locate such mechanisms in a confined area along the net feed path between the net supply and the bale forming chamber.